"Come!" It is a warm, open-handed word to begin with, and the poem's last word is a goodbye. Everything in between explains how an invitation into a gentle evening becomes a parting. The speaker calls a loved one out into an hour of soft winds, then confesses that the world has already worn their heart down. The central idea is that tenderness is dangerous. Hearts that open easily get hurt, and the speaker suggests that the only refuge, a brief walk under the trees with someone faithful, cannot last.
The poem's key move comes in its first two stanzas. The opening scene is calm: "Soft Zephyrs breathe gently around," and an anemone, called "night-boding," has "sunk its pale head on the ground." The flower droops where we might expect it to bloom. The second stanza then turns the flower into a person: a "mild heart that expands to its blast" is torn by the world. The same weather has become violent, with the gentle breeze replaced by a "blast." The verb "expands" matters, because opening up is exactly what makes a flower, or a heart, vulnerable. "Keenness" appears twice in quick succession, and the word suggests both a cutting edge and a sharp wind. The world is imagined as weather with a blade in it.
The sound of the poem works against its sorrow. Every quatrain rhymes ABAB (hour/flower, around/ground, and so on), and the rhythm is a light, rocking triple beat: "Soft Zephyrs breathe gently around." It moves like a tune, which suits a poem titled "Song" but sits oddly beside words like "wretched forlorn." The effect is to make grief sound sweet, as though sadness is being turned into music as it happens. The last stanza breaks the pattern slightly with its short opening line, "Then! dearest farewell." The line is clipped and the rhythm drops a beat, like a hand letting go.
One printing detail is worth noticing. The third stanza runs straight into the one about the trees with no gap, so it looks like eight lines. The rhymes (woe/me/low/thee, then moon/you/soon/adieu) show that these are two separate quatrains. The poem is built from tidy units even where the layout hides them.
The trees give the poem its most interesting image. They "wave past the moon" in their "umbrage," meaning their shade, and "all declare I must part with you soon." The verb "wave" does double duty, since the branches also seem to be waving goodbye, and they "bid you a tender adieu." Nature here is a witness that seems to know the lovers' future. The speaker never gives a reason for the separation. No quarrel, journey or obstacle is named, so the parting feels like fate rather than a decision. The softness of "may ne'er meet again" leaves a thread of doubt. As printed, the line also contains a small puzzle: "You and I love, may ne'er meet again" reads most naturally if "love" is a term of address, so that the speaker is saying "you and I, love, may never meet again."
The ending returns to the opening. "Sweet" and "soft" from the first stanza come back in "how soft and how sweet was the strain." A "strain" is a musical phrase, and "was" puts the love firmly in the past. The woods and meadows "can tell" of it, so the landscape becomes the keeper of the memory, and the poem itself becomes that remembered strain.
As for significance, the poem is a clear and compact example of a familiar kind of sentimental lyric. A flower stands for a heart, nature mirrors feeling, and the language is stocked with words like "forlorn" and "neglected." Readers who know Shelley's more ambitious writing may find this one modest, and its stock phrases suggest a poet working within an established mode rather than breaking it. But that makes it useful for study. You can see how the pattern is assembled: a gentle scene, a turn to a human lesson, a personal confession, and a farewell witnessed by the landscape. The poem also shows how rhythm and rhyme can make a sad subject sound beautiful, and that tension is what stays with you.